Soliton Diffusion

A decade ago, diffusive motions of solitons were vigorously investigated. Particularly those in <it>trans</it>-polyacetylene were studied extensively in experiments as well as in theoretical works. Unfortunately, however, the problem is still open and we need further works to understand the mechanisms which give rise to the diffusive motion. Developments in early days are reviewed and present status is analyzed. Remaining problems and future possibilities are discussed.